This invention relates to electric heating elements for injection molding systems and more particularly to spacer clips for properly locating the heating elements.
As is well known, the adequacy of the provision for heating in an injection molding system is critical to its satisfactory performance. Accordingly, the concept of casting an electrical heating element into a heater cast is well known in the art, one example of which is shown in the applicant's previous U.S. Pat. No. 4,222,733 wherein an electrical heating coil is cast into a beryllium copper heater cast. This structure has the advantage that it provides for the rapid dissipation of heat away from the heating element and for its relatively even distribution along the hot runner passage.
However, in order to provide for optimum heat flow characteristics, while maintaining the necessary structural strength, it is essential that the coils of the heating element be accurately located with respect to one another and in the heater cast. In the past, this has been provided by using a spacer plate to locate the heating element coils during casting which extends in a vertical plane from the coils to the outside of the cast over a considerable portion of the height of the cast. This plate has had the disadvantage of forming a vertical fault line in the cast which has resulted in an unacceptable failure ratio when the heater cast is subjected to repeated high loading forces during use.
In order to overcome this problem, it is necessary to provide for the accurate and reliable location of the heating element coils during casting without unduly weakening the structure of the heater cast or other body into which the heating element is cast.